I'm a huge believer in the FN SLP gas operated shottie...why not take every advantage?
But if you are determined to stay with a pump gun, I'd highly recommend the Vang Comp conversion paired with the Low Recoil ammo.
It has been a couple of years since the class, but there were attendees who came with all the various available stocks. We all got a chance to shoot each others guns and the Vang Comp was the clear winner in controlability in a pump gun, followed closely by ammo selection
...because the journey is the worthier part...The Shepherd's Tale